The invention relates to a semiconductor mask correcting device and a semiconductor mask correcting method of correcting a defective portion of a photo mask, which is used in the process of fabricating a semiconductor device, into a non-defective photo mask.
Since a photo mask used in the process of fabricating a semiconductor device is an original form of a pattern, an existence of a defective portion is necessarily inspected and the defective portion is appropriately corrected as needed, after a mask pattern is drawn on a mask substrate.
In a fabrication method of a usual photo mask, first, design data of the mask pattern is designed by using a computer, and then the designed data is transformed into drawing data for a drawing device. Next, a drawing of the mask pattern is performed on a mask substrate by the drawing device on the basis of the drawing data. Due to this, the photo mask a mask pattern of which is drawn on the mask substrate can be made.
Additionally, after making the photo mask, it is possible to check an existence of a defect of the photo mask or a location of the existence of that by using a defect inspecting device, and when the defect exists, a semiconductor mask correcting device performs the defect correction before transferring an image of the mask to a wafer.
As for the defects of the mask pattern, there are examples such as an extrusion which is projected as an extra protrusion from a desired pattern, and an intrusion which is a concave portion such as an empty on the desired pattern. The mask correction device specifies a location by finding the defective portions, and appropriately corrects them. In methods of the correction, for example, when the protrusion is found, the protrusion portion is corrected by a focused ion beam to be cut off (i.e. an etching process). Additionally, when the concave is found, the concave portion is corrected by gas assist method so that a predetermined material is deposited therein (i.e. a deposition process).
In addition, as for a method of inspecting the mask pattern, there are usually two ways available. That is, systems of a die to die and a die to database are available.
The die to die system is a method which is used when the same mask pattern of at least two or more is drawn on the mask substrate, and finds the defective portion from differences between the patterns by matching them to each other. The die to die system has advantages that an inspection time is short and comparatively performed in a simple way, while the system does not cope with the defective portion occurring in the same way on all patterns and the case of drawing only one pattern on the mask substrate.
Particularly, a pattern shape which is subjected to the correction becomes a fine size and a complicated shape in company with a decrease in size of a semiconductor device, recently. Therefore, it is difficult to compare the pattern shape with an original design of that. That's reason why a die to database system is required more and more instead of the die to die system.
The die to database system is a method comparing a mask image acquired by scanning a mask pattern which is actually drawn on the mask substrate with drawing data stored as CAD data, by using a pattern matching.
Using this method, an actual pattern and a designed pattern can be compared by being directly matched (piled up) to each other, and thus the defective portion such as the protrusion or the concave portion is detected in high accuracy. Thanks to this, the die to database system will be a mainstream as an inspection method from now on.
Recently, accompanied with a decrease in size of the semiconductor circuit, an optical proximity effect correction (i.e. OPC) which is one of the kinds of a resolution enhancement technology (i.e. RET) such as phase shift mask technology is just applied in the semiconductor mask fields. That is a technology using a mask for improving a transfer characteristic by controlling a phase and a transmittance of light, and OPC patterns such as a serif, a jog, and a hammer head are added on the mask pattern. In this way, even if the mask pattern is a fine pattern, it is possible to obtain a desired transfer image by using exposure.
Particularly, the transfer image transferred by the mask pattern is mostly used in a semiconductor circuit. Hence, such a method is also employed to obtain a high-accuracy semiconductor circuit.
Additionally, in addition to the OPC pattern recently, a method adding an assist pattern which is an application of the OPC pattern is contrived to expose an edge of the mask pattern more accurately (see, for example, Benjamin G. Eynon, Jr.: “Photomask Fabrication Technology”, McGraw-Hill ELECTRONIC ENGINEERING, 2005, Chapter 7: Resolution Enhancement Techniques, P457-P467).
The assist pattern which is occasionally called a different name as SRAF (i.e. Sub Resolution Assist Feature) is mostly arranged to surround a vicinity of the main pattern to become a circuit pattern. The assist pattern has a characteristic that it is formed excessively thinner than the main pattern, and the pattern itself does not resolve during exposure, but when the main pattern around which the assist pattern is disposed is exposed, highly accurate transfer is enabled by solving fluctuation of the edges of the main pattern. That is, the assist pattern functions as auxiliary of the main pattern.
As mentioned above, to fabricate the fine semiconductor circuit in high accuracy, a method using a mask pattern which combines the assist pattern with the main pattern is just employed recently.
The assist pattern is disposed in accordance with a shape of the main pattern, and thus design data of the main pattern is designed first, then the assist pattern is inserted by being designed in accordance with the main pattern. Next, the pattern designs of the main pattern and the assist pattern are employed as final circuit diagram data, and then the final circuit diagram data is transformed into the mask data which is drawing data. The photo mask is fabricated by drawing on the mask substrate in accordance with the mask data.
After making the photo mask, the photo mask and the mask data is compared by the die to database system which is directly matched to each other, and the correction is appropriately performed along with the inspection of the defective portion such as the protrusion and the concave portion.
However, there are the following problems that still remain in the assist pattern mentioned above.
First, the final circuit diagram data adding the assist pattern to the main pattern transforms into the mask data which is the drawing data through a process usually called a fracturing. Because of the reason, all pattern data of the final circuit diagram data is minutely partitioned in the form of a trapezoid and a rectangle.
In particular, as shown in FIG. 9, a recent main pattern MP is formed in a complicate shape by adding the OPC pattern thereto as mentioned above. Therefore, through the fracturing process, the main pattern on data is recognized as an aggregate of a plurality of the trapezoid or the rectangular shape partitioned as shown in FIG. 10.
On the contrary, as shown in FIG. 9, the assist pattern AP is arranged around the main pattern MP in a comparatively thin and rectangular shape with a certain width, but it has a simple shape compared with the main pattern MP, and thus the assist pattern is recognized as just own shape itself as shown in FIG. 10 after the processing.
By the way, since the main pattern MP is recognized as an aggregate of shapes such as a rectangle, the main pattern can not be distinguished from the assist pattern AP on data. That is, as shown in FIG. 10, a part of figure mp forming the main pattern MP takes the same shape by comparison with the assist pattern AP, so there is a concern about an error recognizing the part of figure mp as the assist pattern AP.
Accordingly, in a step of mask data, the main pattern MP and the assist pattern AP can not be clearly recognized to be distinguished between them. Additionally, the mask data is stored into a mask data file in a partitioned state.
Accordingly, when the die to database system is attempted to inspect the photo mask after drawing on a substrate in actual situation, it is difficult to match the mask data with a photo mask image in high accuracy, and thus the inspection of the defective portion can not be performed.
Above all, since, as for the main pattern of the photo mask, the transfer image becomes semiconductor circuit when exposure is performed, it is necessary to match with the main pattern MP of the mask data in high measurement accuracy and location accuracy to inspect the defective portion, and properly correct by specifying the defective portion. However, since the main pattern MP can not be distinguished from the assist pattern AP on the mask data as mentioned above, it is not possible to inspect the main pattern which is required after the drawing.
In addition, even if it is possible to distinguish the main pattern MP of the mask data from the assist pattern AP, it is difficult to match the main pattern in high accuracy in an actual situation.
In detail, since the assist pattern AP stored as the mask data is mostly designed as a fine line shape different with the main pattern MP (to prevent resolving in the process of exposure), it is easily affected by a distortion during drawing on the mask substrate. Therefore, the assist pattern drawn in actual situation becomes distorted shape, and mostly, does not necessarily match with the assist pattern AP of the mask data. However, the assist pattern is not resolved even though the exposure is performed, so it is allowed even if there are some defective portions or errors. Accordingly, there is commonly no correction for the drawn assist pattern. That is, the correction of the photo mask is commonly performed for only the main pattern.
Because of that, when the photo mask image is matched with the mask data, it is required to inspect the defective portion by matching between locations of both main patterns only in high accuracy.
However, when the photo mask image and the mask data is subjected to the pattern matching, the high distorted assist pattern is formed on the photo mask as mentioned above, whereupon it adversely affects matching of the main pattern. For example, it is attempted to perform as the high distorted assist pattern of the photo mask is compulsory matched with the assist pattern AP of mask data, or the high distorted assist pattern of the photo mask is compulsory matched with the main pattern MP of the mask data since it is failed to correctly recognize the assist pattern.
As mentioned above, the assist pattern AP of the photo mask is one of the noise factors in the process of matching, whereupon an accuracy of matching decreases. Accordingly, the matching of the main pattern can not be performed in high accuracy, and it is not possible to exactly perform the inspection and the correction on the defective portion.
In is an object of the invention which is contrived in consideration of the situations mentioned above to provide a semiconductor mask correcting device and a semiconductor mask correcting method capable of performing the pattern matching process which matches the photo mask having the assist pattern with the mask data in high accuracy by using a die to database system, and fabricating the photo mask with high quality by performing the mask correction in high accuracy.